The present invention relates to a liquid-crystalline resin composition that is excellent in mold-releasing property when used for molding and that has decreased possibility of deformation or fracture when a molding is released from a mold and to a molding using the same.
Liquid-crystalline resins comprise a poly-domain having a liquid-crystalline state without causing interlocking even in a molten state because of the rigidity of the molecule and show a behavior in which molecular chains are remarkably oriented in the flow direction due to shear during molding. Therefore, they are generally called melt liquid-crystal type (thermotropic liquid-crystal) polymers. Because of this special behavior, the liquid-crystalline resins have significantly good melt flowability. Depending on their molecular structures, they show a high deflection temperature under load and a high continuous-use temperature, and do not cause deformation or blistering when immersed in a molten solder at 260xc2x0 C. or more.
Because of such reason, resin compositions in which a fiber reinforce material represented by glass fiber, an inorganic filler represented by talc and the like are filled in a liquid-crystalline resin are materials suitable for electric or electronic parts having a thin part or a complicated shape. For example, they are used for relay parts, coil bobbins, connectors, volume parts, motor parts such as commutator, separator or the like, or encapsulation for elements such as coil, quartz oscillator, IC tip or the like, and so on.
In the trend towards a light-thin-short-small in recent years, however, thinner and smaller shapes of products have become more strongly demanded, and many products have a thickness of 0.2 mm or less. In moldings having such thin part, molding is very difficult even for liquid-crystalline resins and molding defects such as short shot, flash and the like often occur. In order to avoid these defects, it has been necessary to increase injection rate or pressure. This requires higher pressure to be applied on a product upon removing the product from a mold, or on release from a mold. As a result, problems occasionally occur such as where the product is deformed or fractured on being released from a mold, depending on a shape of the product or the structure of a mold, resulting in size-precision failure of the product or a fractured piece formed during production being left in a mold. The latter produces significant decrease in productivity due to the need to temporarily stop production in order to remove the piece.
For solving these problems, attempts have generally been carried out such as use of a composition in which a lubricant is added to a resin and external addition of a lubricant to a resin. Examples of generally used lubricant include metal salts of aliphatic acids, aliphatic acid amides, lower molecular weight polyolefins and the like. JP-A 2-208035 discloses a method in which an aliphatic acid ester is added to a liquid-crystalline polyester; JP-A 4-120162 discloses a method in which a polyhydric alcohol or the like is added to a thermoplastic polyester; JP-A 10-505109 discloses a method in which a polyethylene having a molecular weight of 1,000 to 10,000 is added; and JP-A 7-233310 discloses a method in which an olefin polymer having a molecular weight of 10,000 to 600,000 is added.
In the case of resins having a high processing temperature like liquid-crystalline resins, however, the lubricants as described above are thermally decomposed or evaporated during processing. Therefore, sometimes physical properties are adversely affected, or no or insufficient effect is obtained. In addition, problems may occur that blisters are generated on the surface or inside part of a product during molding.
Accordingly, a purpose of the invention is to suppress the problems of size-precision failure due to deformation of the product during molding, decrease in productivity due to blister defect or fracture and the like, and to provide a liquid-crystalline resin composition excellent in mold-releasing property and a molding obtained using the same.
As the result of extensive studies conducted in order to solve the above-described problems, the present inventors have found that the above purpose can be attained by a composition in which an ultra-high molecular weight polyethylene having a molecular weight of a specific value or more is added to a liquid-crystalline resin, and successfully have completed the invention.
Therefore, the invention provides a liquid-crystalline resin composition comprising 0.01 to 10 parts by weight of an ultra-high molecular weight polyethylene having a molecular weight in excess of 600,000 and 100 parts by weight of a liquid-crystalline resin that exhibits an anisotropic liquid-crystalline state in a molten state.
The invention also provides a molding obtained by molding the above-described liquid-crystalline resin composition.